1. Field of the Invention
The present invention relates to improvement of the adhesion between a copper-based material and a sealing resin which are used in a semiconductor device.
2. Description of the Background Art
High adhesion to a copper-based leadframe or wiring pattern may be used for a sealing resin used in a semiconductor device, in order to establish compatibility between a recent request on the semiconductor device for high reliability against humidity, heating/cooling cycles, vibration, etc. and a recent request on the semiconductor device for cost reduction.
In the background art, there has been known and used a technique in which a silane coupling agent is mixed into an epoxy-based sealing resin by an integral blending method (internal addition to the resin) in order to improve the adhesion between the sealing resin and the copper-based leadframe or wiring pattern.
In addition, in order to ensure stable adhesion between a copper-based material and a sealing resin, an oxide film may be present in the surface of the copper-based material (see Technical Reports of Fukushima Technology Center Research P. 71-77 1992 and Koya Nomura and Hiroshi Sakamoto, “Adhesion Characteristics of Copper Alloys to Mold Resin as a IC Leadframe”, Kobe Steel Engineering Reports, Vol. 48, No. 3, December 1998, p. 21-24). On the other hand, since the copper surface is apt to be oxidized, the surface is normally treated with an antioxidant in order to prevent an adverse effect on the adhesive force or to aggressively improve the adhesion.
The silane coupling agent exhibits a reaction mechanism as shown in FIG. 5, and has a hydrolyzable group having affinity or reactivity to an inorganic material such as the copper-based leadframe and an organic functional group making a chemical bond to an organic synthetic resin etc. in a molecule. Accordingly, mechanical strength, water resistance, adhesion, etc. in an interface between a composite material (such as blending of a silica filler into an epoxy resin) and the copper-based leadframe can be improved by a function of bonding the organic material and the inorganic material to each other. The proper quantity of usage of the silane coupling agent on that occasion can be obtained by empirical examinations.
For example, in JP-A-9-124901, a semiconductor sealing epoxy resin composition which contains a predetermined crystalline epoxy resin, a flexible curing agent, a curing accelerator, an inorganic filler, an unsaturated double bond-containing silane coupling agent, and a mold release agent as essential components has been disclosed as a technique relating to a semiconductor sealing resin.
When a relatively large amount of a silane coupling agent is blended into an epoxy resin, there is a problem that some of the silane coupling agent stays unreacted in the resin to cause hydrolysis of the epoxy resin to thereby lower the adhesive force, the elastic modulus and Tg of the epoxy resin. Accordingly, it is necessary to obtain the blending quantity of the silane coupling agent by empirical examinations.
In addition, when the copper-based leadframe or wiring pattern is used, the adhesion high enough to satisfy the high reliability request cannot be ensured simply by addition of an optimal quantity of the silane coupling agent. Further, as described above, an oxide film may be present in the copper surface in order to ensure stable adhesion between the copper-based leadframe or wiring pattern and the sealing resin. However, the relation between the kind of copper (an additive etc.) or the composition or film thickness of the oxide film and the adhesive force to the epoxy resin has not been made clear yet. Further, when the copper-based leadframe or wiring pattern is treated with an antioxidant, there is a drawback that the resin will be decomposed in the adhesive interface in a moisture-resistance and heat-resistance test.